Effects of Pulsed Laser Deposition Conditions on the Microstructure of Ca3Co4O9 Thin Films

The influence of deposition conditions on the microstructure of Ca₃Co₄O₉ (CCO) thin films fabricated by the pulsed laser deposition technique was investigated. X-ray diffraction revealed that a fast deposition rate resulted in not only low crystallinity but also the existence of the Ca _x CoO₂ secondary phase. The Ca _x CoO₂ structure was further confirmed by high-resolution transmission electron microscopy. The CCO thin-film growth was deduced to be a kinetically controlled process, and the quality of the thin films strongly depended on the coalescence process. The formation of Ca _x CoO₂ was inevitable during the thin-film growth. However, given enough time and supply of oxygen at a lower deposition rate, it was possible to transform the Ca _x CoO₂ phase into the desired CCO phase during the coalescence process, while with faster deposition, more Ca _x CoO₂ structure was formed, and the secondary phase could hardly transform into the CCO phase.